Lbr 



Mn 



l\lx- 



MOUTH-PARTS OF A COCKROACH 15 



and differ both in their origin and in their mode of action 

 from the jaws of Vertebrates. They work from side to side, 

 and not up and down, nor backwards and forwards. 



The mandible of the cockroach, as of other insects, is simple 

 and unjointed ; it is articulated by a condyle, and again by a 

 small cup, to separate parts of the head. The free end is 

 armed with strong, tooth-like processes. The maxilla of the 

 first pair lie behind the man- 

 dibles. In each we can 

 make out a two - jointed 

 basal part, a five-jointed 

 palp, which is used in feed- 

 ing and exploration, and 

 two terminal pieces, set side 

 by side. These last are the 

 galea and lacinia ; the galea 

 (external piece) is soft in the 

 cockroach ; the lacinia (in- 

 ternal piece) is hard, curved, 

 and armed with a two-pronged tooth. The maxillse of the 

 second pair are fused to form the labium, a hanging flap, 

 which closes-in the mouth behind. The broad shield-like base 

 is divided into an upper and larger piece, the submentum, 

 and a lower piece, the mentum. A pair of three-jointed palps 

 are attached to the sides of the mentum, and parts answering 

 to the galea and lacinia of the first pair of maxills will be 

 easily recognised. It is evident that the labium consists of 

 a pair of appendages, similar to maxillse, but fused together 

 in the middle line. 



Mxp 



-Diagram of jaws of cockroach, in 

 horizontaLsection , 



4. (PRACTICAL.) DISSECTION OF A COCKROACH* 



Kill with heat (see Lesson 2). Cut off the wing-covers and 

 wings (if present). Hold the insect in the hand, and with fine 

 scissors cut round the edges of the dorsal surface. Remove 

 the dorsal integument thus detached. 



Examine the under side of the dorsal integument. The 



* A fuller account of the anatomy of the cockroach will be found in 

 Marshall and Hurst's ' ' Practical Zoology, " or Miall and Denny's ' ' Structure 

 and Life-History of the Cockroach." 



